:-consult(grammar-2).  % grammar rules have the format LHS ---> [RHS]

parse(X,[s(X)], []).                        % Success state.

parse(X,Stack, L):-                      % If TOS corresponds to a RHS,
     reduce(Stack, [], NewStack),      % reduce the stack
     parse(X,NewStack, L).               % parse the new stack

parse(X,Stack, [Word|L]):-               % If TOS is word,
     parse(X,[Word|Stack], L).           % read it, push it and recurse.

reduce(Stack, RHS, [LHS|Stack]):-      % The accumulator matches RHS
     (LHS ---> RHS).                   % so LHS is pushed
reduce([NT|Stack],Acc,NewStack):-      % If it does not, pop NT to Acc
     reduce(Stack,[NT|Acc],NewStack).  % and recurse.